Explore Atrial Fibrillation

What Is Atrial Fibrillation?

Atrial fibrillation (A-tre-al fi-bri-LA-shun), or AF, is the most common type of arrhythmia (ah-RITH-me-ah). An arrhythmia is a problem with the rate or rhythm of the heartbeat. During an arrhythmia, the heart can beat too fast, too slow, or with an irregular rhythm.

AF occurs if rapid, disorganized electrical signals cause the heart's two upper chambers—called the atria (AY-tree-uh)—to fibrillate. The term "fibrillate" means to contract very fast and irregularly.

In AF, blood pools in the atria. It isn't pumped completely into the heart's two lower chambers, called the ventricles (VEN-trih-kuls). As a result, the heart's upper and lower chambers don't work together as they should.

People who have AF may not feel symptoms. However, even when AF isn't noticed, it can increase the risk of stroke. In some people, AF can cause chest pain or heart failure, especially if the heart rhythm is very rapid.

AF may happen rarely or every now and then, or it may become an ongoing or long-term heart problem that lasts for years.

Understanding the Electrical Problem in Atrial Fibrillation

In AF, the heart's electrical signals don't begin in the SA node. Instead, they begin in another part of the atria or in the nearby pulmonary veins. The signals don't travel normally. They may spread throughout the atria in a rapid, disorganized way. This can cause the atria to fibrillate.

The faulty signals flood the AV node with electrical impulses. As a result, the ventricles also begin to beat very fast. However, the AV node can't send the signals to the ventricles as fast as they arrive. So, even though the ventricles are beating faster than normal, they aren't beating as fast as the atria.

Thus, the atria and ventricles no longer beat in a coordinated way. This creates a fast and irregular heart rhythm. In AF, the ventricles may beat 100 to 175 times a minute, in contrast to the normal rate of 60 to 100 beats a minute.

If this happens, blood isn't pumped into the ventricles as well as it should be. Also, the amount of blood pumped out of the ventricles to the body is based on the random atrial beats.

The body may get rapid, small amounts of blood and occasional larger amounts of blood. The amount will depend on how much blood has flowed from the atria to the ventricles with each beat.

Most of the symptoms of AF are related to how fast the heart is beating. If medicines or age slow the heart rate, the symptoms are minimized.

AF may be brief, with symptoms that come and go and end on their own. Or, the condition may be ongoing and require treatment. Sometimes AF is permanent, and medicines or other treatments can't restore a normal heart rhythm.

The animation below shows atrial fibrillation. Click the "start" button to play the animation. Written and spoken explanations are provided with each frame. Use the buttons in the lower right corner to pause, restart, or replay the animation, or use the scroll bar below the buttons to move through the frames.

Types of Atrial Fibrillation

Paroxysmal Atrial Fibrillation

In paroxysmal (par-ok-SIZ-mal) atrial fibrillation (AF), the faulty electrical signals and rapid heart rate begin suddenly and then stop on their own. Symptoms can be mild or severe. They stop within about a week, but usually in less than
24 hours.

Persistent Atrial Fibrillation

Persistent AF is a condition in which the abnormal heart rhythm continues for more than a week. It may stop on its own, or it can be stopped with treatment.

Permanent Atrial Fibrillation

Permanent AF is a condition in which a normal heart rhythm can't be restored with treatment. Both paroxysmal and persistent AF may become more frequent and, over time, result in permanent AF.

What Causes Atrial Fibrillation?

Atrial fibrillation (AF) occurs if the heart's electrical signals don't travel through the heart in a normal way. Instead, they become very rapid and disorganized.

Damage to the heart's electrical system causes AF. The damage most often is the result of other conditions that affect the health of the heart, such as high blood pressure and coronary heart disease.

The risk of AF increases as you age. Inflammation also is thought to play a role in causing AF.

Sometimes, the cause of AF is unknown.

What Are the Signs and Symptoms of Atrial Fibrillation?

Atrial fibrillation (AF) usually causes the heart's lower chambers, the ventricles, to contract faster than normal.

When this happens, the ventricles can't completely fill with blood. Thus, they may not be able to pump enough blood to the lungs and body. This can lead to signs and symptoms, such as:

• Palpitations (feelings that your heart is skipping a beat, fluttering, or beating too hard or fast)


• Shortness of breath


• Weakness or problems exercising


• Chest pain


• Dizziness or fainting


• Fatigue (tiredness)


• Confusion

Atrial Fibrillation Complications

AF has two major complications—stroke and heart failure.

Stroke

During AF, the heart's upper chambers, the atria, don't pump all of their blood to the ventricles. Some blood pools in the atria. When this happens, a blood clot (also called a thrombus) can form.

If the clot breaks off and travels to the brain, it can cause a stroke. (A clot that forms in one part of the body and travels in the bloodstream to another part of the body is called an embolus.)

Blood-thinning medicines that reduce the risk of stroke are an important part of treatment for people who have AF.

Atrial Fibrillation and Stroke

The illustration shows how a stroke can occur during atrial fibrillation. A blood clot (thrombus) can form in the left atrium of the heart. If a piece of the clot breaks off and travels to an artery in the brain, it can block blood flow through the artery. The lack of blood flow to the portion of the brain fed by the artery causes a stroke.

Heart Failure

Heart failure occurs if the heart can't pump enough blood to meet the body's needs. AF can lead to heart failure because the ventricles are beating very fast and can't completely fill with blood. Thus, they may not be able to pump enough blood to the lungs and body.

Fatigue and shortness of breath are common symptoms of heart failure. A buildup of fluid in the lungs causes these symptoms. Fluid also can build up in the feet, ankles, and legs, causing weight gain.

Lifestyle changes, medicines, and procedures or surgery (rarely, a mechanical heart pump or heart transplant) are the main treatments for heart failure.